Missed or late?!

Abigail
When is a period considered late and missed? I hear different things and want to see what y'all think or know. 
I am 2 days late, I think that's the correct term used. I was due for a period the 13. Took a test its negative. My back aches, hip/pelvis pain, peeing more frequent. I woke up yesterday with spotting and then nothing since. Any ideas?!